Engineering thermoplastics are a class of materials that exhibit high performance in terms of their mechanical and thermal properties as well as chemical resistance. Generally derived from expensive monomers, these polymers are produced in relatively low volumes and are more costly compared to aliphatic thermoplastics. In terms of chemical architecture, engineering thermoplastics are comprised at least in part of aromatic groups and polar moieties, deriving their superior properties from strong interactions between chains as well as intrinsic bond strengths. Also contributing to their performance, many engineering thermoplastics are semi-crystalline in nature, including poly(ether-ether-ketone) (PEEK), polysulfides (PSF), polysulfones (PSU), polyphenylene sulfide (PPS), poly(ether-ketone-ketone), and polyamides. The superior properties of these materials provide them as viable lightweight substitutes to metals in many demanding applications.
In general, to achieve the optimal mechanical properties and environmental durability inherent to engineering thermoplastics and composite structures made from such materials an adequate degree of polymer crystallinity needs to be achieved. Processing conditions ultimately control observed microstructures in this class of materials and while polymers achieve full crystallinity with processes imposing adequate annealing times, only a fraction of the potential crystallinity is developed with rapid manufacturing techniques characterized by polymer cooling through the glass transition temperature from the melt state in seconds. Therefore, it would be cost-effective to develop a means to increase the crystallization rates of engineering thermoplastics for the sake of fabricating structures with methods imposing rapid processing cycle times.
Engineering thermoplastics can often be difficult to process due to their high melt viscosities, a direct result of the intrinsic polarity of the chemical groups that comprise the polymer backbones coupled with their relative chain stiffness. With conventional polymer processing methods, viz. compounding, extrusion, and injection molding, high temperatures and robust equipment are generally necessary for component production. In the particular case of carbon fiber composite fabrication, high viscosities impede the diffusion of polymer chains between layers of laminates which may result in less than optimal mechanical properties of the ultimate composite. Thus, it would be beneficial to develop a means to reduce the viscosities of engineering thermoplastics without sacrificing the properties that set them apart from other types of polymers.
Thus, it would be desirable to increase the crystallization rates of engineering thermoplastics for rapid fabrication of structures, products and components thereof. And there is need and market for same, which overcomes the above prior art shortcomings.
There has now been discovered a method for increasing the crystallization rate of engineering thermoplastics to provide well formed and durable plastic products made in rapid processing cycles.